Woodgas Can Stove

Introduction: Woodgas Can Stove

This is a design for an inexpensive, lightweight wood-burning stove, suitable for backpacking, bike touring, and bush cooking.

It is a two-wall design, which preheats air in between the walls to ignite the smoke. Well-tended, this produces a bright, smokeless flame which produces little soot and leaves little to no scorching on the ground below.

It is built from commonly available (in the United States) parts: a quart paint can, a smaller tin can, and a shorter tin can. The only specialized tools are a safety-style can opener and an Irwin Unibit #1, though similar designs can be made with just a church-key and ordinary can opener and alternate tools are discussed in appropriate steps.

The whole thing can be built in about an hour. This model weighs 6.6 oz (187 grams) after several firings, and nests in, e.g., the Snow Peak 900 Ti or Al pot.

Ready? You'll need:

Step 1: Materials

A 1-quart paint can, with lid. I just bought a new one for a couple bucks at the local hardware store; if you're reusing one with paint in it you need to fire the paint off in an open fire. This is nasty and you're probably better off buying a new can.

A 19 ounce Progresso soup can. Other cans such as 20 ounce cans of fruit will work as well, but the Progresso cans are a bit shorter, which we want.

A Large, short can. Mine had bamboo shoots in it; many cat foods and canned meats come in this sort of can. The diameter should be a little larger than the inner ring on top of the quart can. Don't get an aluminum one, it'll melt and buckle in the heat.

Step 2: Tools

You'll need:

Drill

Tin Snips

Irwin Unibit #1 Though one can use several bits to make successively larger holes, this tool will make you life easy and your holes better.

Safety Can Opener This is the kind that takes the top entire off the can, rather than cutting a hole in the top. One could use the other kind but this will leave a jagged hole and isn't recommended.

Also useful

Sharpie, Electrical Tape and Scissors for marking where the holes go. The ruler turned out useless, however a:

Fabric Tape Measure proved very useful indeed.

Step 3: Drill the Bottom Sides of the Inner Can

This step I will be doing differently in the next model.

What I did here was drill two rows of 1/4" holes in the bottom side walls of the can. This does not provide enough draft. A design known to work, this stove's closest relative in fact, has holes in the bottom, rather than the bottom sides, so one could drill out a bunch of quarter-inch holes into the bottom.

I intend to drill out another can in the near future, with three rows of 3/8" holes up the inner walls, and perhaps more holes as well. I'll update this instructable accordingly, and welcome comments on people's luck with this step.

Step 4: Measure Top Holes of Inner Can

The circumference of your can is in the area of 10 1/2". What you're going to do is mark 10 spots an inch apart, leaving one area with a slight gap between the holes.

The quarter-inch fabric measure is about a quarter-inch from the top corrugation of the can; this gives a good result.

Step 5: Drill the Top Holes

Drill holes into your dots, all the way down to the bottom of the unibit. Let the rotation, rather than the pressure, do the cutting, or you'll get some buckling.

Step 6: Measure Holes in Outer Wall

The outer can is about 13 1/4" in circumference. We measure 10 holes, an inch apart. leaving a gap between them. I centered this gap on the seam, because it looks nice, but this isn't necessary.

5/8" up from the rim turns out to be the sweet spot for the holes. An eighth inch either way won't kill ya.

Step 7: Drill Holes in Outer Can

Make 1/2" holes in the can on your marks. You have to look at these holes, so take your time and do it right and you'll have a neat-looking stove.

Step 8: Remove Bottom of Outer Can

Take your safety cutter and remove the lid. It can be reserved for extra fire protection or discarded as useless; take your pick.

Step 9: Press Fit Cans Together

Taking your soup can, press the top rim into the inside-top rim of the quart paint can. It'll be a tight fit, push it in there with the heel of your hand until you feel it lock into place. No additional fastening is necessary; to crimp the seal, pound the lid back on as far as it will go with a rubber mallet. Be prepared to spend quite awhile prying the lid off with a flat-head screwdriver after!

Step 10: Drill Out Potstand/windscreen

Make a diamond-pattern of 3/8" holes, as shown.

Leave room to cut a feed slot out.

Step 11: Cut and Crimp Feet Slot

With tin snips, cut out a chunk of the can to make a hole to feed sticks into the fire while a pot is on it. With your multitool or pliers, crimp the edges in to strengthen the cut and reduce the chances of snagging a finger.

Remove the bottom of the can with your safety opener, and discard.

Slice through the top, leaving a ring that can be stored between the walls or nested into the top ring of the can.

Step 12: You're Done!

This one came in at 6.6 oz or 187 grams, but drilling more holes in the inner can should drop a couple points while making it work better. This compares with the BushBuddy, which weights 6.4 oz and costs 90 bucks Canadian, while offering similar functionality.

Step 13: Use It!

To fire up your cooker, you will first need a can full of biomass. Best choice is pencil-sized sticks of completely dry, dead wood, most often found still attached to trees or hanging from branches. Anything which is laying on the ground is likely to be somewhat damp, hindering a clean burn. The stove will also burn charcoal, pine cones, bits of cane etc. to varying degrees of success.

Fill the can with sticks, laid parallel to the ground in alternating rows like a grid. Bring the wood to near the top burner holes, but do not cover them.

Place the cooker on something that won't ignite, and shelter it from the wind. You could carry a windscreen but unless you're traveling in particularly harsh terrain it's worth it just to find a quieter place to cook your meal.

Build and start a small fire on top of this fuel. Fire-lighting is an arcane art with many approaches, all of which call for some practice and skill. A general approach that works well is a tinder ball with a small tipi of sticks around it; the idea is to get the sticks burning and start to char the layer below, as well as to make glowing coals that drop down to ignite the lower wood.

Place the windscreen/potstand in the groove of the can; this can be used to build a lean-to style top fire as well. Experiment before it makes the difference between dinner hot and dinner cold!

If properly built and loaded, the stove will ignite the smoke from the fire readily, within a minute of ignition. When the smoke is burning cleanly and brightly, it's time to put a pot on the stand. I keep steel chopsticks on hand to stir the fire if needed, but a light hand is best here and the fire if well built will burn without interference.

When the existing wood has all become coal, one can keep the fire going by feeding sticks in one at a time. They quickly ignite and the smoke feeds the fire for awhile; the stove in this mode must be frequently but lightly fed, finding a balance between too much smoke to burn it all and not enough to keep the secondary burn going.

I keep the lid around, as a trivet for the pot, and to cover the fire when i'm done with it. This will cause the remaining charcoal to smother out slowly; leaving the lid off will led it burn down into clean ash. The can could be used for charcoal making by firing it until the volatiles are mostly gone, covering the bottom holes with dirt, and putting the lid on.

As I implied earlier, the stove as shown here doesn't work as well as it might. I chalk this up to the small holes at the bottom of the inner can; larger holes, and more of them, will feed the fire properly and keep everything nicely aglow.

Step 14: Credits

The first stove of this nature I'm aware of is the Bushbuddy, http://www.bushbuddy.ca/. By all reports it works well, I've never had a chance to use this or any other woodgas stove but my own. It is expensive, but first in class.

This design closely models http://tjamrog.wordpress.com/2008/12/22/the-evolving-backpacking-wood-stove/, by Tim Jamrog. His design has holes in the bottom of the inner can, rather than the bottom sides, and this is known to work well. I'm working on a design with a solid bottom, for various reasons including catching the ash and embers. As I've indicated, it works, but it could work better, and I think larger holes on the sides of the inner can will help. For just under six bucks in materials, experimentation is easy.

For those wanting the lightest weight and blingiest gear, the Bushcooker LT from http://www.fourdog.com/index_files/bushcooker.htm can't be beat. Titanium won't rust out, ever, and the LT II, which is closest in size to this model, weighs a wispy 3.5 oz.

Making stoves is easy, fun and satisfying. Experiment to your heart's content, and let me know what you come up with.

Built one today, and did a burn test. It was pretty easy to build, not my cleanest work, but smooth on the outside, and serviceable for backpacking. The test burn was sans water, and I was happy to see no issues, and a burn time of as long as I wanted to keep adding scrap wood, about 45 minutes. After I do a test with water, I'll post a comment as well. I did opt to drill out the bottom of the inner chamber instead of the sides.

This is a great instructable. I will be building one of these to take camping for sure. That being said, I think this may be misnamed. Wood gas is actually a completely different thing altogether. http://en.wikipedia.org/wiki/Woodgas This is more like a really complicated chimney starter. http://en.wikipedia.org/wiki/Chimney_starter I have actually cooked on my chimney starter before when quickly searing tuna and steaks and I can completely appreciate this design as a means to concentrate heat and cook things quickly and efficiently.

It would be interesting to pit a chimney starter modified with a potstand against this stove to see which would boil water faster.

To quote the Wiki on the subject of woodgas:
"Certain designs of stove, are in effect a gasifier working on the updraft principle - the air passes up through the fuel, which can be a column of rice husks, and is combusted, then reduced to carbon monoxide by the residual char on the surface. The resulting gas is then burnt by heated secondary air coming up a concentric tube. Such a device behaves very much like a gas stove. This arrangement is also known as a Chinese burner."
That's the sort of stove this is! I hope that was clear. This stove is also not unlike a chimney starter.

Pstretz was right: This is a wood stove, not a wood gasifier. A gasifier creates two products: wood gas and charcoal; it requires heat from another fire to operate. The wood is not actually burned in a gasifier.

In making this good stove, I couldn't remove the tab-opening Progresso can lid with any of my can openers, because the rim is too high. Surveying available canned goods, I found another source for 19-ounce cans, measuring the same as the Progresso but with an ordinary top and bottom, in the ethnic section: La Victoria brand enchilada sauces (both red and green types) come in three sizes, including the one we need for this purpose. Just thought folks might like to know.

I built the stove!. Great instructions.In the inside can I made two rows of holes on the sides and did a fair amount of perforation on the bottom.I am definitely getting wood gas burning. However, I am also getting flames deep in the can.I think I have too many holes in the lower end of the inner can. Is a large airy area in the bottom of the can too much?

if you used the bottom you removed from the outer can and cut tabs in the inner can. Then cut and bend the outer can bottom down so it would bend down and catch on the tabs you made in the inner can, also between 10 to 12 holes must be drilled in this piece. Then bend tabs back up to secure the bottom you reused from the outer can.Now you have a more efficient stove and easier to light and keep lit stove.

When the inner can heats up wont that expand the metal, thus weakening the friction hold on the two cans? After one burn i would think a simple drop on a table would make the two can seperate... But of course i may be wrong...

I made one of these and its actually very tough. Believe me it does get hot, but the two pieces fit together so tightly and so perfectly, it's as if they were made to go together. I found that I had to hammer the two pieces together because they fit so tightly. i have used it on many occasions, from car-camping trips to wilderness backpacking, and never worried for a seconds about the structural integrity.

You could have it burn better by adding a grill-type floor/level inside your burning can, slightly higher then the airholes at the bottom. This will have the fire air-fed from below. Making a more efficient burn, while ash will find it's way through the grill. The sticks will lean on the grill-floor which optimizes airflow. Your fire will reach optimum temperature a bit faster.

The penny-wood stove (http://www.csun.edu/~mjurey/pennywood.html) uses a grid of much smaller holes all across the bottom and one optional ring around the outside. The lower they are, the longer/better each charge of wood will produce wood-gas, so on the bottom is probably the best location.

Ideal might be several big openings on the bottom and a wire mesh bottom dropped into the bottom of the can to spread out the ventilation manifold.

Wonderful! a cheap, easy to make, effective, and most importantly lightweight stove! put this together this afternoon, only i punched holes in the bottom of the inner can. i think once i make those holes a tad larger (the primary burn wasnt getting enough air, so it kept going out) this will be a great addition to my backpacking gear. as always, i have a suggestion to improve this method:
rather than trying to press fit the cans together by hand (i tried but, ill admit, i wasnt strong enough) i put the cans, one inside the other, upside down on a table and placed another soup can on the bottom of the Progresso can. i then pounded it with a hammer untill the progresso can fit tightly inside the paint can. worked in seconds.
thanks for the awesome design, i cant wait to go backpacking again!!

Great instructable. On my inferior attemps at woodgas stoves I found using a small birthday candle was a good way to gently light the top of the twigs by using it like a match- the drips helping it to burn. Sort of cheating on the 100% renewable fuel I know, but convenient!

Great tutorial, I seriously mean that. I do have a question about this step though. Everything else you did looks very neat and tidy, but here everything looks a bit ragged. This is not meant as a criticism. I was just wondering what happened. Is it maybe the cutting tool or the thin can wall or something? This might help me to select different materials when I build mine.
Great work.

Two things happened here...
One is the can is a cheap Chinese piece of crap :-) hey, it got the bamboo shoots here, so it did its job! I even dropped it before I opened it, denting one of the sides slightly. The quality of the steel is one reason the holes are jagged.
The other reason it's on the raggedy side is the tin snips I was using are the kind that look like a parrot's beak Use the kind that look like a robin's beak instead.
Other people have had good results building the pot stand out of stainless steel mesh. Ordinary hardware cloth will burn through in a matter of days.

Fact is It's tough to drill holes cleanly in ANY sheet metal, that 's why holes in sheet metal in commerial production runs are generally punched. Expanded metal will last far longer than hardware cloth, but expanded metal can be very tough to work with. Not being critical of your project, but inserting food for thought for other's.

Efficiency is a tricky concept. A fan will make for a stronger burn under more conditions, at a penalty of extra weight, moving parts, and a battery which must be replaced or topped up from time to time. This stove doesn't need a fan, and properly built, fueled and fired is capable of a clean, mostly soot-free flame.
Bloody Wesley, the 19 oz soup can locks into the inner ring of the quart paint can. It's a really neat hack; the inner can is held in place the same way the lid of the paint can is, by deforming the inner lip of the paint can to fit. Others have used more 'durable' fastenings, but I see no point; it takes real force to wedge that can in there.
As mentioned in the instructions, using a rubber mallet to pound the lid on after press-fitting the cans will make the joint even tighter, though make sure you have a nice flat-head screwdriver or butter knife on hand to pry that lid back off!

I spin fire now :)
Thanks for the upload- seems a simple design, but ideal for the job- nice one! if you could lace the wood burning tin with a little fire cement, it'll add a little more weight, but it'll last longer- just a tip, if you ever wanna use this set up for drying clay, or art purposes.

I've considered stove paint for durability; fire cement might be a bit bulky, which is more of a concern than weight, but a thin layer might well do it.
Right now i'm going with the philosophy that a) most people building similar stoves haven't burned them out and b) soup cans are cheap. :-) If I end up with rust problems that may change.

If you're referring to the "Bushwhacker" woodgas stove, then yes, it's a similar design, although this stove is more like a BushBuddy or Tim Jamrog's can stove.
I intend to take photos and video of the burn process, but first I'm going to make a new inner burn chamber and modify the instructable accordingly. Definitely want those larger holes at the bottom of the inner can sides!